Compressed metal oxide product

ABSTRACT

The present invention relates to a bound metal oxide particle comprised of metal oxide and a binder, with the binder preferably being a starch solution. The present invention also relates to a method for forming a bound metal oxide particle, with the preferred method including extruding and pelletizing a metal oxide and binder composition to form pelletized metal oxide particles.

FIELD OF INVENTION

The present invention relates to a bound or compressed metal oxideparticle for use in removing contaminants, including sulfur compounds,from fluids, and a method for making such compressed metal oxidecomposition. More preferably, the present invention relates to anextruded pelletized iron oxide composition, with the binder being astarch composition.

BACKGROUND OF INVENTION

It is well known to use metal oxides, particularly iron oxide (Fe_(x)O_(y)) in a reactor bed to remove contaminants, typically sulfurcompounds, especially hydrogen sulfide (H₂S), from fluids, typically gasstreams. Sulfur compounds are removed from fluids because they are knowncontaminants, which potentially make gas streams or other fluidsunsalable. Gas that contains too much sulfur is known as sour gas. Assuch, in the gas industry, as well as related industries, it isconsidered necessary to remove sulfur compounds from fluids, includinggas. Note that these fluids are typically devoid of oxygen. (It is knownoxygen can increase reactivity between a metal oxide composition andcontaminants.) For this reason, there is a need for products that removesulfur compounds efficiently and cost effectively from fluids. It isfurther desired to have a method or composition that does not requirethe inclusion of activating agents, such as oxygen. Unfortunately, mostcommercially available iron oxide compositions (the most frequently usedmetal oxide material in removing sulfur) which operate at ambientconditions and are generally non-activated, hold an amount of sulfurequal to at most 20% by weight of the total iron oxide composition. Moretypically, iron oxide material (like that compressed in the presentprocess) will hold on average 0.12 lbs of H₂S/lb of iron oxide. (Thepercent held is dependent, in part, on the particular species of ironoxide used). Increased H₂S absorption capacity for iron oxidecompositions, above 20%, typically require the addition of a caustic oroxygen to the feed gas, which is dangerous and potentially difficult,especially at high pressures. This is problematic because approximately80% of the total metal oxide product is unused. For this reason,frequent replacement of the metal oxide is required. Consequently, it isdesired to increase the percent by weight of sulfur held by the totalmetal oxide product.

Sulfur removal on a level that treats up to millions of cubic feet ofgas per day or on an industrial scale, typically requires the use oflarge reactor beds filled with the iron oxide media or product.Typically, this media is comprised of iron oxide and a carrier such asmontmorillonite or wood chips. In order to eliminate frequentchange-outs, that is the replacement of spent metal oxide media (mediathat no longer has suitable reactivity with sulfur) with new metal oxidemedia, large or numerous reactor beds are used. These reactor beds willeither be very tall, 10 feet or higher, or multiple reactors will belined up in succession so that a plurality of reactor beds will be used.If the reactor beds are too small or few, the metal oxide will be spenttoo fast. This is because when treating large volumes of gas or otherfluids, the metal oxide found in the metal oxide media will be rapidlyreacted. In order to have a sufficient bed life so that frequentchangings of the metal or iron oxide media is not required, largeamounts of metal oxide must be used. This is disadvantageous for acouple of reasons. First, the amount of sulfur held by the metal or ironoxide composition is low relative to the total weight of the productused. In order to increase efficiency, it is desired to have a productthat holds a greater percentage of reacted sulfur per pound of totalproduct. Secondly, the amount of area required to remove sulfur canincrease costs. It is desired to have the option to decrease the totalarea required to remove H₂S. In other words, it is desired to hold agreater amount of sulfur with a decreased amount of metal oxidecomposition.

One way to increase the amount of sulfur held in a reactor vessel is topelletize or compress the metal oxide. The amount of sulfur held by themetal oxide composition is increased because there is more availablemetal oxide in the vessel. Normally, metal oxide is placed on a carrier,with the carrier comprising approximately 80% by weight of the metaloxide composition. Conversely, a pellet is typically comprised of anamount of binder equal to from about 1% to about 20% by weight of thepelletized mixture. As can be seen, the amount of metal oxide issignificantly increased. The binders that have been used to form thepelletized iron oxide particles include cement, bentonite, and similarcompositions, especially inorganic compositions. The pelletizedparticles made from these binders, however, have suffered from a problemin that it appears that the efficiencies have been lowered and that thereactivity of the metal oxides has been decreased. In particular, theamount of sulfur held is not significantly increased over the amount ofsulfur held by the same species of metal oxide particle on a carrier.For this reason, prior attempts to pelletize metal oxide have beenconsidered unsuccessful because of inadequate sulfur reactivity, inparticular, holding capacity. Thus, it is necessary to find a binderthat allows for sufficient binding of the metal or iron oxide particleswithout lowering the reactivity or efficiency with which the sulfurcompounds are removed. More particularly, it is necessary to find abinder that permits the metal oxide to hold a greater amount of sulfur,in particular, H₂S, without the presence of a caustic or the addition ofoxygen in some form.

As stated, it has been known to pelletize metal oxides for use inremoving sulfur compounds from fluids. In particular, U.S. Pat. No.4,732,888, invented by Jha et al. discloses a zinc ferrite pellet foruse in hot coal gas desulfurization. The patent discloses a compositioncomprised of zinc and iron oxide bound together with inorganic andorganic binders, and a small amount of activator. Inorganic bindersinclude bentonite, kaolin, and Portland Cement. The organic bindersinclude starch, methylcellulose, and molasses. The pellets have a veryspecific product design because they are used in beds havingtemperatures of at least 650° C. Because of the high temperatures, theorganic binders dissipate leaving pellets that are fragmented andporous. Thus, the organic binders are included for the specific purposeof holding the pellets together, initially, and then dissipating so asto create greater porosity. While this design is outstanding for use inhigh temperature coal desulfurization processes, it does not provide forsufficient removal at ambient conditions. As implied, it has beenobserved that inorganic binders decrease the amount of sulfur removed bypelletized metal oxides. As a result, insufficient removal of sulfurwill likely occur at ambient or near ambient conditions when inorganicbinders are used to bind the pellets together. It should also be noted,that it has previously been believed that organic binders wereunacceptable for forming pellets used at ambient conditions, because theorganic binders generally do not provide for a pellet that hassufficient crush strength, or there is insufficient reactivity, or theuse of the binders creates a pellet that is cost prohibitive.

SUMMARY OF INVENTION

The present invention relates to bound or compressed metal oxideparticles used in the removal of contaminants, preferably sulfurcompounds, from fluids and methods related thereto. The compressed metaloxide particle will be comprised of an amount of metal oxide equal to atleast 80% by weight of the compressed metal oxide particle.Additionally, the compressed metal oxide particles have a crush strengthequal to at least 1.0 kg and, more preferably, a crush strength equal toat least 3.5 kg. The compressed metal oxide will also retain an averageamount of sulfur equal to at least 10% by weight of the compressed metaloxide particle and, more preferably, an amount of sulfur equal to atleast 30% by weight of the compressed metal oxide particle. Importantly,the compressed metal oxide particle will hold a greater amount of sulfurthan if the particular metal oxide species used to form the compressedmetal oxide particle was used in association with a carrier. Generally,the compressed metal oxide particle will be able to hold an amount ofhydrogen sulfide (H₂S) equal to at least 0.27 per pound of metal oxideparticle. The compressed metal oxide particle is further advantageousbecause it will sufficiently remove sulfur at temperatures of less than150° C. and, even more advantageously, at ambient conditions.

The compressed metal oxide particle will be comprised of an amount ofmetal oxide, preferably in powder form or having a small particle size,and a binder. The metal oxide will have a particle size ranging betweenabout 0.1 microns and about 100 microns, which means that the metaloxide will be similar to dust, also known as fines. Any of a variety ofmetal oxides which are reactive with sulfur compounds may be used toform the bound metal oxide particles. Most preferably, the metal oxidewill be of the formula Me_(x)O_(y), with Me selected from the groupconsisting of row 4, 5, 6, and 7 metals, with x equal to between 1 and3, and y equal to between 1 and 4. It is more preferred if the metaloxide is an iron or zinc oxide composition, as these metal oxides havebeen known to readily react with sulfur compounds. In particular, ironoxide of the formula Fe_(a)O_(b) will be preferred with a equal tobetween 1 and 3, and b equal to between 1 and 4. As such, iron oxide ofthe formula Fe₃O₄ is most preferred.

Any of a variety of organic binders may be used to hold the metal oxideparticles together to thereby form the compressed or bound metal oxideparticle. The binder selected must permit the metal oxide to be reactivewith the sulfur compounds, and must also provide for a bound metal oxideparticle having sufficient crush strength. Crush strength will be equalto at least 1.0 kg, as mentioned above, and is more preferably equal toat least 3.5 kg. As such, it has been determined that a suitable binder,which provides for a bound metal oxide particle complying with thepresent invention is a starch composition. A starch composition will becomprised of anywhere 0.5% to 20% by weight starch, with the remainderof the composition comprised of water. Additionally, lignin, bentonite,and lignosulfonate may also be used as binders. The binder can be addedto the metal oxide in an amount equal to between 0.5% and 20% by weight,and more preferably in an amount equal to between 0.5% and 5% by weight.

The method of the present invention involves combining the starch andthe metal oxide particles and thoroughly mixing the two constituents.Once the two constituents are mixed, it is necessary to compress thecomposition so as to form the bound metal oxide particles. Thetechniques used to compress the constituents to form the bound metaloxide particles can be any of a variety of techniques or devices. Anycompression device or method can be used as long as the bound metaloxide particles are suitably formed and have sufficient crush strength.It is most preferred, however, to pass the constituents through anextruder to form an extruded metal oxide composition. This has beenfound to produce pellets or particles which have sufficient crushstrength and reactivity with contaminants, especially sulfur compounds.Additionally, once the material has been extruded, it is preferred topelletize the material so as to form pelletized, extruded metal oxideparticles. Any of a variety of extrusion devices may be used as long asthe particles or pellets will have a diameter ranging between 3 mm and20 mm, and a length ranging between 3 mm and 20 mm. More preferably, thepellets will have a diameter of approximately 3 mm to 6 mm, and a lengthof about 6 mm.

The present invention is advantageous for a number of reasons. Inparticular, the bound metal oxide particles allow for a product that canbe used in a reactor bed, whereby the product reacts with a greateramount of sulfur so that a greater amount of sulfur is found in thereactor bed. This is desirable because a lesser amount of overall spacecan be used and fewer reactor vessel change-outs are required. Thepresent invention is also advantageous because it demonstrates that apelletized and extruded metal oxide particle can be formed that hassufficient reactivity with sulfur. This means that the particles aresuitable for commercial use unlike many other known pelletized metaloxide compositions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 describes removal of various sulfur compounds from a propaneliquid stream using pelletized iron oxide with measurements taken,initially, at 6 hours, 14 hours, and 22 hours;

FIG. 2 describes the same thing as FIG. 1, except a zinc oxidecomposition was used to remove the sulfur compounds;

FIG. 3 is a graph which relates three flow rates to a k (Bran's)constant versus lbs. of H₂S on an oxide bed;

FIG. 4 describes the same thing as in FIG. 3, except it compares threedifferent types of iron oxide;

FIG. 5 describes the same thing as FIG. 3, except it relates to adifferent type of iron oxide;

FIG. 6 discloses a comparison between non-pelletized iron oxide and twotypes of pelletized iron oxide, whereby outlet H₂S is related to thepounds of H₂S on the oxide bed; and,

FIG. 7 relates to the same thing as in FIG. 6, except it compares threedifferent types of pelletized iron oxide.

DETAILED DESCRIPTION

The present invention relates to a bound or compressed metal oxideparticle, a method for making such particle, and a method of using suchparticle to remove contaminants, preferably sulfur compounds, fromfluids. The bound metal oxide particle is preferably an extrudedpelletized iron oxide particle that is well suited for removing sulfurcompounds, such as H₂S, from fluids. The pelletized extruded metal oxideparticle advantageously retains a greater amount of the sulfur compoundsthan other metal oxide compositions. The pelletized extruded metal oxidecan retain an average amount of sulfur equal to at least 10%, andpreferably 30%, by weight of the pelletized extruded metal oxideparticle. Preferably, an extruder is used to form the pelletizedextruded metal oxide particle, which is comprised of at least one metaloxide and a binder. The preferred binder is a starch based composition.

The method is initiated by mixing an amount of metal oxide with anamount of binder to form a homogenous metal oxide blend. Any method ofmixing the two constituents can be used so long as the constituents arethoroughly mixed and a homogenous binder, metal oxide blend is formed.It is preferred to add the binder to the metal oxide in an amount equalto from about 0.5% to about 20% by weight of the metal oxide. Morepreferably, the starch binder is added to the metal oxide in an amountequal to between 0.5% and 5% by weight of the metal oxide.

Any of a variety of metal oxides can be used in the present invention,with the metal oxides defined by the formula Me_(x) O_(y), whereby Me isselected from the group consisting of row 4, 5, 6, and 7 metals, with xequal to between 1 and 3 and y equal to between 1 and 4. Morepreferably, the metal oxide is selected from the group consisting ofFe_(a) O_(b,) ZnO, and combinations thereof, with a being equal tobetween 1 and 3 and b equal to between 1 and 4. Also, hydroxides of themetal oxide may be used. Iron oxide compositions (Fe_(a) O_(b)) are themost preferred metal oxides for use in the present invention.Preferably, the bound metal oxide particle will be comprised of Fe₃ O₄.This composition is commonly sold under the name “black iron oxide” andas such, black iron oxides are preferred for use in the presentinvention.

The metal oxide will have a particle size ranging between about 0.1microns and about 100 microns and, more preferably, between about 1.5microns and 50 microns. As such, the unprocessed or raw metal oxide usedto form the bound metal oxide product will be fines, or in powder form.Thus, a uniform body or bound particle will be formed from a granular orfine material.

Most preferably, the iron oxide will be ferrimagnetic. It is believedthat the iron oxide particles that provide the best results are not onlyferrimagnetic, but have a particle size ranging between about 0.1microns and about 100 microns. More preferably, the particle size willrange between about 1.5 microns and about 50 microns. Also, theparticles are preferably porous so that they are believed to have atleast 25× more surface area than other non-porous particles such assolid particles of the same size. These are believed to be desiredcharacteristics.

The binder that is mixed with the metal oxide should be of a sufficientbinding strength so as to form a metal oxide particle that will have acrush strength of at least 1.0 Kg, and preferably 3.5 Kg, as measured bya Kohl hardness tester. Not only should the binder impart a sufficientcrush strength, but it should be such that it does not impact thereactivity of the metal oxide particles with sulfur. It is hypothesizedthat the binder should be such that it allows for the bound metal oxideparticles to have some porosity or transfer capability, which allowsreasonable use of the interior of a particle. Regardless, the bindershould allow the pelletized metal oxide to retain an amount of sulfurequal to at least 10% by weight of the pellet and preferably at least30% by weight of the pellet. Any of a variety of binders fitting thisdescription can be used; however, it is most preferred to use an organicbinder that is more preferably a starch solution. A starch solution canbe comprised of anywhere from 0.5% to 20% by weight starch, morepreferably from between 0.5% to 15% by weight starch, with the remainderof the solution comprised of water. A starch solution of thisconcentration will allow for an amount of starch equal to at least 0.25%by weight on a dry weight basis of the metal oxide particle compositionto be present in the metal oxide particle, with as much as 5% starchpresent in the metal oxide particle composition. It is preferred if thestarch present in the metal oxide particle composition is equal to orless than 3%. Besides starch, lignin, bentonite, and lignosulfonate canbe used as a binder.

In addition to the metal oxide used to form the bound metal oxideparticle, an amount of activator of metal oxide can be added to themixture. The addition of the activator is intended to increase thereactivity of the bound metal oxide particle and, in particular, willcause the particle to more readily react with sulfur compounds. Amongthe available activators are copper oxide, silver oxide, gold oxide,platinum oxide, cadmium oxide, nickel oxide, palladium oxide, leadoxide, mercury oxide, tin oxide, cobalt oxide, aluminum oxide, manganeseoxide, and combinations thereof. It is most preferred, however, to use acopper oxide, as this has been known to most readily increase thereactivity of a metal oxide without the ready formation of hazardouscompounds, as specified by the Environmental Protection Agency. Theactivator should be added in an amount equal to from about 0.5% to about5% by weight of the metal oxide composition used to form the bound metaloxide particle.

Once the metal oxide composition has been mixed, the metal oxidecomposition is compressed to form the bound metal oxide particle.Compression can be achieved in a variety of ways as long as boundparticles are formed. It is preferred to pass the composition through anextruder device or a similar device so as to form an extruded metaloxide composition. Any of a variety of extruders and methods can be usedfor forming the extruded metal oxide so long as sufficient reactivitywith sulfur is maintained and the particles produced therefrom havesufficient crush strength. It is preferred if the die on the extruderhas a diameter ranging between 3 millimeters (mm) and 20 mm, and adieway length of at least 15 mm. Generally, the length will be 5× thediameter. It is believed that these die conditions will result in aparticle having sufficient reactivity and crush strength. It is morepreferred for the die length to be at least 30 mm long and 6 mmdiameter.

Once the extruded metal oxide passes through the die, it is preferred tochop or cut the extruded material into particles to form pellets.Standard methods in the industry for forming pellets out of extrudedmaterial can be used. As such, the preferred pelletized, extruded metaloxide material will have a crush strength of 3.5 Kg, a diameter rangingbetween about 3 mm and about 8 mm, and a length ranging between 15 mmand 40 mm. Note that the crush strength of the pellets will be dependentupon a variety of factors including moisture content, starchconcentration, die diameter, and die length.

Besides extruding the metal oxide and the binder, other compressed formsmay be used. Among the available compressed forms are pellets, tablets,pestilles, ribbed, ribbed rings, rings, spheres, and extrusions.

Any method for compressing the metal oxide together so that a carrier isnot required and it can be used in a reaction bed can be used. It isfurther desired to form pellets instead of simply adding metal oxidepowder to a reaction vessel because for sufficient reactivity to occur,there must be space within the reactor to allow the fluid to pass.Powder would not allow for a sufficient flow rate.

After the pellets are formed, it is necessary to dry the pellets so asto reduce moisture. Any process for drying can be used so long as thepellets have a total water content of less than 10% by weight, and, morepreferably, less than 3% by weight. The temperature used to dry thepellets should be any temperature that will not breakdown or incineratethe binder and which does not oxidize the metal oxide. Preferably, thetemperature will be 150° C. or less and, more preferably, thetemperature will be 90° C. or less. It is necessary to dry the pelletsto maximize the crush strength.

Dryers that may be used include a rotary dryer or belt dryer. The rotarydryer is preferred.

It is preferred to then marumerize the pelletized extruded metal oxideparticles as this has been found to increase the hardness, abrasion asmeasured by the percentage of fines in the treated pelletized extrudedmetal oxide. Any of a variety of marumerizers may be used in the presentinvention. Rotary drying may eliminate the need for a marumerizer.

Once the pelletized extruded metal oxide particles have been formed,they should be placed in a reactor vessel so as to be contacted withfluids contaminated with sulfur compounds. The fluids will include gas,liquid, and combinations thereof. It is most preferred to remove sulfurcompounds from contaminated gas streams, such as propane and hydrocarbongases. Among the sulfur compounds that can be removed using the presentmetal oxide particles are hydrogen sulfide (H₂S), carbonyl sulfide(COS), carbon disulfide (CS₂), Dimethyl Sulfide (DMS), and mercaptans,such as Methyl Mercaptan (MeSH), Ethyl Mercaptan (EtSH), and PropylMercaptan (PrSH). It should be noted that it is likely that othercontaminants found in fluids, especially hydrocarbon gas, can be removedby the compressed metal oxide particles. These sulfur compounds can beremoved under ambient conditions, more particularly, when thetemperature is equal to or less than 70° C., with 200° C. being thehighest temperature. Any pressure can be used, with ambient pressurepreferred. Additionally, the fluid stream can be passed over the metaloxide particles at a velocity equal to at least 0.6 feet per minute, ingases and 0.1 feet per minute for liquids.

The compressed metal oxide particles can retain an average amount ofsulfur equal to at least 10%, and preferably 30%, by weight of the boundmetal oxide particles and have an H₂S holding capacity equal to at least0.27 pounds of H₂S per pound of metal oxide product. Also, the metaloxide particles should have a density ranging between 1.0 and 1.5. Fromthis, it can be concluded that the pelletized extruded metal oxideproduct has increased sulfur holding capacity.

The following examples are for illustrative purposes only and are notmeant to limit the claims in any way.

EXAMPLES Example 1

A test was conducted to determine the effectiveness of extrudedpelletized iron oxide in removing sulfur species contaminants,including, hydrogen sulfide, carbonyl sulfide, mercaptans, and possiblycarbon disulfide. The test was initiated by packing a 2 inch by 12 inchcolumn with approximately 1.25 pounds, or approximately 10 inches, ofpelletized iron oxide media. The iron oxide pellets were comprised ofblack iron oxide and a starch binder. An inlet valve was located at thebottom of the column so that contaminated liquid entered the column atthe bottom and exited the top of the column. The gas to be purified wasliquid propane contaminated with various sulfur species contaminants,including hydrogen sulfide, carbonyl sulfide, and light mercaptans.Measurements to determine the amount of sulfur contaminants were madewhen the gas entered the column and when the gas exited the column, withmeasurements taken at different times. FIG. 1 shows the initial amountsof various sulfur compounds entering the column. The contaminants weremeasured in parts per million by weight, or PPMW. The specificconditions in the reactor or column are listed below as follows:

Type of Treater Single, Verticle Flow Direction Up Flow Treater Temp 65°F. Contact Time 15 mLs/min L/D Ratio 5:1 CEP-1 FM1 Extrusion SamplePressure 360 PSIG

L/D stands for Dieway length/Diameter in the die of the extruder.

The sulfur contaminants were detected by using a copper strip test,which identified the amount of sulfur and contaminants in the liquidstream, by its corrosivity to polish copper strips by ASTM methodD-1838.

As can be seen from FIG. 1, the pelletized iron oxide resulted inexcellent removal of various sulfur compounds. In particular, H₂S wasreadily removed by the pelletized iron oxide. Additionally, COS, CS₂,and mercaptans were readily removed. Thus, it was concluded that thepelletized iron oxide provided for excellent removal of sulfurcompounds. This was considered important because it was known thatprevious iron oxide pellets did not sufficiently remove sulfur, ascompared to iron oxide on a carrier.

Example 2

The same procedure as Example 1 was followed except pelletized zincoxide was tested instead of pelletized iron oxide. The conditions wereas follows:

Type of Treater Single, Verticle Flow Direction Up Flow Treater Temp 65°F. Contact Time 11 mLs/min L/D Ratio 5:1 CEP-1 2.0 extrusion SamplePressure 360 PSIG

The results of the test are disclosed in FIG. 2. It was observed thatthe pelletized zinc oxide, in general, removed most sulfur compoundsexcept COS. Use of the pelletized zinc oxide resulted in suitableelimination of most sulfur compounds. This was considered importantbecause normally zinc oxide suitably eliminates sulfur contaminants athigher temperatures. At ambient conditions, zinc oxide will typicallyhold between 3% and 8% total sulfur.

Example 3

Tests were conducted to determine the relative crush strength ofpelletized iron oxide particles. Three types of iron oxide known as FM1(Ferrimagnetic 1), FM2 (Ferrimagnetic 2), and Hoover were pelletized,with all three types of iron oxide being similar black iron oxides. TheFM1 and FM2 iron oxides are ferrimagnetic porous iron oxide particlesbelieved to range in size from 1.5 microns to 50 microns, with ahypothesized surface area of 10 m²/gm. The Hoover oxide is believed tobe a much smaller grade material with little or no porosity. The ironoxide was blended with various types of binders, with the binders mixedin different amounts in solution. Also, various extruder die lengthswere used. These variations were made to determine what combinationwould result in iron oxide particles having sufficient crush strength. Apelleting press manufactured by Kahl was used to form all the iron oxidepellets, with the pellets formed from the press having a diameter of 6mm. To assess the strength of each pellet, a Kahl Pellet Hardness Testerwas used. In order to derive accurate data, tests were made on tenpellets manufactured according to each method, with the results thenaveraged. The Kahl pellet tester is manufactured by Amandus Kahl Gmblt &Co., Hamburg, Germany. The following table shows the results of thetests, the particular type of binder for use in forming each of thepellets, the die length used to form the pellets, and the average crushstrength.

TABLE 1 LCI TEST SUMMARY Water Dieway Strength Oxide % Binder* Length kgDensity Fines FM1 18.2 None 18 Weak 1.690 FM1 15 None 18 Weak 1.448 FM115 0.0075% CMC 18 Weak 1.406 FM1 15 None 36 Weak 1.477 FM1 12 0.0075%CMC 36 Weak 1.542 FM1 13 0.0075% CMC 36 Weak 1.508 FM1 13 0.0075% CMC 48Weak 1.475 FM1 13 0.0075% CMC 60 Weak 1.454 FM1 13 0.64% Starch 30Fragile 1.359 FM1 16 0.78% Starch 30 Firm — FM1 17 0.84% Starch 30 3.8 —FM1 15 12.5% Bentonite 30 4.3 1.542 Hoover 17 1.0% Starch 30 5.1 — FM217 1.0% Starch 30 1.6 — FM1 19.2 1.34% Starch 60 — — FM1 17.3 1.33%Starch 60 5.1 — FM1 17.2 1.33% Starch 60 5.98 — FM2 15.3 1.04% Starch 603.1 1.33  15.1 FM2 15.3 1.04% Starch 60 1.9 1.45  7.6 FM2 18.8 2.36%Starch 60 6.65 1.17  5.3 FM2 18.8 2.36% Starch 60 4.7 1.46  2.4 FM2 18.92.34% Starch 48 7.65 1.03  3.2 FM2 18.9 2.34% Starch 48 8.3 1.32  1.3FM2 18.9 2.34% Starch 48 6.8 1.23  1.8 FM2 18.9 2.34% Starch 36 6.01.06  2.1 FM2 18.9 2.34% Starch 36 6.05 1.23  1.7 *Binder % on basis ofdry weight oxide

The binder listing is the percentage of starch on a dry weight basisfound in the pellets. The percent water represents the amount of binderand water solution mixed with the metal oxide material. The density ofthe pellets appears to be unrelated to the crush strength of thepellets.

As can be seen from the data, the use of starch and bentonite providedfor excellent crush strength in the pellets formed therefrom.Carboxymethylcellulose resulted in a pellet having insufficient crushstrength. Additionally, it was determined that a die length of at least30 mm was preferred.

Example 4

The present Example relates to testing the pelletized FM1, FM2, andHoover iron oxides to evaluate the reactivity and efficiency of eachcomposition in removing hydrogen sulfide from gas. Three reactor bedswere filled with the three different types of iron oxide. Two pounds ofthe pelletized iron oxide material was placed in a 4-foot glass reactorbed tube. This step was repeated for each test composition listed inTable 2. A sour gas stream containing 3,000 parts per million by weight(ppm) of H₂S was passed over the various pelletized iron oxidecompositions. Specifically, the gas was passed over the FM2 bed once,the FM1 bed three times, and the Hoover bed three times, all of whichare listed in the chart below. The flow rate of the contaminated gas (Q)was set at one of three different rates: 2.09 liters per minute (L/min),3.75 L/min, or 5.09 L/min. The outlet H₂S was recorded as a function oftime of the varying flow rates.

FIG. 6 shows how much H₂S was held on the Hoover and FM1 types of ironoxide at flow rate of 2.09 L/min before break-through of H₂S occurred.Additionally, FIG. 6 shows how much sulfur was held on the same type ofiron oxide used to form the FM 1 composition, but with the iron oxidelocated on a carrier. As can be seen, the pelletized iron oxide heldsignificantly more sulfur. In FIG. 7, the same thing as FIG. 6 wasshown, except a different flow rate, 5.09 L/min, was used. The systemwas pressurized at 6 PSIG, and the sour gas had a temperature of 68° F.The H₂S was measured using an industrial scientific TMX 412 electronicgas analyzer, calibrated with a standard 124 parts per million H₂S intube mixture. Also, a Kitagawa tube was used as a cross check to confirmthe H₂S levels.

The rate constants (k) were calculated from a determination of theoutlet H₂S, with the outlet H₂S (lbs.) equation as follows: Σ[H₂Sreacted over Δt (lbs.)]. FIG. 3 plots the rate constant versus thepounds of H₂S on the bed for FM1 oxide material. Three different flowrates were used. The (Bran's) constant k was highest at the fastest flowrate of 5.09 L/min. The slope of the curve equates to the rate ofreactivity over time. The steeper the curve, the faster the reactivitywill be reduced. Thus the slope of the lines in FIGS. 3, 4, and 5indicate reactivity. FIG. 5 shows the same thing as FIG. 3, except theiron oxide was the Hoover species. FIG. 4 relates to the same data as inFIG. 3, except three different types of iron oxides were tested.

The FM2 had the highest rate of reactivity, followed by the FM1. Bothcompositions showed excellent reactivity. The Hoover material wasobserved to be not as good a candidate for use as the other twomaterials. From the k determination, the estimated per pound capacityfor holding H₂S by the oxide was determined using linear regressionanalysis of a plot of k versus lbs. of total H₂S on the bed. Theestimated capacity is listed below. Further, the slope of the linearregression analysis relates to the speed of reaction between the oxidematerial and the H₂S, this is R. The x intercept of the plots gave theoverall capacity of the materials. The results are summarized asfollows:

TABLE 2 LINEAR REGRESSION ANALYSIS OF K VS. ACCUMULATED LBS OF REACTEDH₂S WITH THE BED Est. Capacity Material Q (L/min) Slope per Pound krange R LCI (FM2) 5.09 −1.6 0.41 1.35-1.15 0.976 LCI (FM1) 2.09 −1.20.30 0.70-0.56 0.992 LCI (FM1) 3.75 −1.5 0.30 0.94-0.72 0.998 LCI (FM1)5.09 −1.4 0.31 0.92-0.70 0.975 LCI (FM1) All data — −1.7 0.27 0.94-0.700.959 LCI (Hoover) 2.09 −2.6 0.17 1.72-0.69 0.982 LCI (Hoover) 3.75 −4.30.15 1.28-0.72 0.998 LCI (Hoover) 5.09 −6.9 0.12 0.90-0.58 0.992 LCI(Hoover) — −5.8 0.13 1.58-0.67 0.984 all data

As can be seen, the FM2 and FM1 had superior results for holding anamount of H₂S per pound of iron oxide (see Est. Capacity per Pound).

Example 5

The reaction rate k, from Example 4, was analyzed to determine whetherthe pelletized iron oxide had a better reaction efficiency thannon-pelletized iron oxide. FIG. 6 is a combined plot of outlet H₂Sreadings (PPM) v. pounds of H₂S that has reacted with a bed ofpelletized material, either the (FM1), (Hoover), or non-pelletized ironoxide materials, at a flow rate of 2.09 L/min. These curves relate tothe outlet readings of H₂S (PPM) to the amount of reacted H₂S with thebed, and directly illustrates the reactive speed of the materials.

As can be seen FIG. 6, two pounds of FM1 product reacted with 0.38pounds of H₂S before the outlet H₂S reached 900 parts per million. Thisis compared with non-pelletized iron oxide, which had only 0.15 poundsof iron oxide reacted before the H₂S reached a level of 900 parts permillion at the outlet. This shows that the pelletized iron oxide gives asuperior result and reacts with a greater amount of H₂S thannon-pelletized iron oxide.

Example 6

The present Example compared pelletized zinc oxide with Sulfatreat®(iron oxide on a montmorillonite carrier). The conditions and resultsare as follows:

ZnO SulfaTreat Bed Height 2.0 ft 2.0 ft Pressure 5 psig. 5 psig. FlowRate 270 cc/min. 270 cc/min. Temp 70° F. 70° F. Inlet Conc. 3000 + ppmH₂S in N₂ 3000 ppm H₂S Diameter 1.5 in. 1.5 in. Weight 1065 gms 827 gmsVolume 815 mL 815mL Total gas used 12830 L 14774 L Total H₂S removed38.5 L 44.3 L Days to Breakthrough 33 38

The ZnO ran for 33 days before hydrogen sulfide broke through. This is 5days shorter than SulfaTreat ran at the same conditions. Although theZnO did not remove as much sulfur as SulfaTreat, the results arepositive. ZnO is mainly used at elevated temperatures and this test wasrun at room temperature and still removed H₂S.

Example 7

The present Example relates to the preparation of exemplary metal oxidepellets used in the removal of sulfur from fluids. The method wasinitiated by obtaining a sample of black iron oxide from the IronriteProducts Company, Inc. of St. Louis, Mo. The black iron oxide wasanalyzed and determined to contain an amount of moisture equal to 3% byweight. Additionally, it was determined that the black iron oxide had abulk density of 1.558 kg/L.

To form the metal oxide pellets, 9,000 gms of the black iron oxideplaced in a bladekneader, manufactured by Sigma Corporation, St. Louis,Mo. To the black iron oxide, an amount of binder solution was added. Thebinder solution was formed by mixing 118 gms of starch manufactured byArgo to boiling water. Starch was measured so that it was equal to 1.34%by weight starch on a dry weight basis, so that the total bindersolution added to the black iron oxide was equal to 17.2% by weight.This formed a binder and iron oxide composition, which was then kneadedin the bladekneader for 5 minutes. A dough was produced that wasslightly wet and sticky.

The iron oxide dough was then fed into a pellet press, Model 14-175(manufactured by Kohl). The pellet press operated at 100 rpm and wasequipped with a 6 mm die, having a 60 mm pressway length. The energyinput for the pellet press was equal to about 1.51 kw, and the extrusionrate was equal to 224 kg per hour.

After extrusion, the pellets were processed in a marumerizer (made byLCI Corporation, Charlotte, N.C.),with an 8 mm friction plate turning at300 rpm for 10 seconds. The pellets were then oven dried at atemperature of about 200° F., and it was determined that the pellets hada bulk density of approximately 1.25 kg/L. Additionally, it wasdetermined that the pellets had a hardness equal to about 6.0 kg.

Thus, there has been shown and described a method relating to the use ofcompressed metal oxide compositions for removing contaminants fromfluids and a method for making such compressed metal oxide compositionswhich fulfill all the objects and advantages sought therefore. It isapparent to those skilled in the art, however, that many changes,variations, modifications, and other uses and applications for thesubject compressed metal oxide and methods are possible, and also suchchanges, variations, modifications, and other uses and applicationswhich do not depart from the spirit and scope of the invention aredeemed to be covered by the invention which is limited only by theclaims which follow.

What is claimed is:
 1. A method for forming a bound metal oxide for useat temperatures less than 200° C. having a crush strength of at least1.0 Kg, a diameter ranging between about 3 mm and 20 mm, and capable ofholding an amount of contaminant equal to at least 10% by weight of saidbound metal oxide, said method consisting of: (a) mixing an amount ofmetal oxide having a particle size ranging between 0.1 microns and 100microns and of the formula Me_(x) O_(y) with an amount of binder to forma metal oxide mixture, wherein Me is selected from the group consistingof periodic table row 4, 5, 6, or 7 metals, x is equal to between 1 and3, and y is equal to between 1 and 4 and hydrated forms of said metaloxide; and, (b) compressing said metal oxide mixture to produce saidbound metal oxide.
 2. The method of claim 1 wherein said compressingstep is achieved by passing said metal oxide mixture through an extruderhaving a die length of at least 15 mm, and a diameter of at least 3 mm.3. The method of claim 1 wherein said metal oxide has a particle sizeranging between about 1.5 microns and 50 microns.
 4. The method of claim2 wherein said bound metal oxide is cut to form a pelletized metaloxide.
 5. The method of claim 4 wherein said pelletized bound metaloxide is marumerized.
 6. The method of claim 2 wherein said bound metaloxide is dried at a temperature ranging between ambient and less than150° C.
 7. The method of claim 6 wherein said method includes dryingsaid bound metal oxide in a dryer selected from the group consisting ofa belt dryer and a rotary dryer.